1> a rat
2> a guy who tells the cops or other authorities of wrongdoings
3> The guy in prison movies who winds up being either killed in the prison riot, or getting pounded in the ass untill he dies of rectal trauma

1> You fuckin Stooly ratbastard
2> that fuckin Stooly ratbastard told the cops about the weed!
3> GET THE STOOLY!!!!